Use teamviewer to get access to the machine. The father will have to download that, run the .exe and give you the ID and password but that's all you'd need to do in order to be able to install anything you want. I've helped plenty of autistic people do this and they usually manage it fine.
Another option are the Microsoft Family settings. This is what I use with my son. His Microsoft account is part of
Microsoft family safety and from that I can ban/restrict certain apps and websites, as well as limit his screen time or time with those apps.
If he needs more time, he just pushes a button and it sends me an email. It's fairly easy to use once it's set up.
He might have to create a new email (I don't know if you can add existing accounts to it or convert local user accounts to it) and a new user account on his computer, but realistically that's not a huge deal.